Multi Purpose Gasification (MPG) plants are used for production of syngas through gasification of oil, tars and refinery residues. These feed stocks typically contain a lot of inorganic species. As a result of the gasifier operation the raw gas contains about 0.25 percent of soot and other solid compounds. The raw gas is cleaned and cooled in a water quench but despite the intensive cleaning in the quench not all of the solid particles are successfully cleaned out from the raw gas stream.
A venturi scrubber is designed to effectively use the energy from the inlet gas stream to atomize a liquid being used to scrub the gas stream. A typical venturi scrubber consists of three sections: a converging section, a throat section, and a diverging section. The inlet gas stream enters the converging section and, as the area decreases, gas velocity increases. Liquid is introduced either at the throat or at the entrance to the converging section. The inlet gas, forced to move at extremely high velocities in the small throat section, shears the liquid from its walls, producing an enormous number of very tiny droplets. Particle and gas removal occur in the throat section as the inlet gas stream mixes with the fog of tiny liquid droplets. The inlet stream then exits through the diverging section, where it slows down to recover pressure. Particle removal efficiency under certain conditions can reach 99%. However there are still several challenges associated with current venturi scrubber technologies.
For example, there are high pressure losses inside the scrubber. It is well understood that pressure drop increases significantly at higher pressures (˜10 bars). Higher the pressure drop inside the scrubber, higher compression energy is required and makes the system energetically inefficient. Also typically the operational pressures go up to 10 bars, with few exceptions known. It is well known that the collection efficiency goes down with increase in operating pressure. Since most of the new gasifiers proposed operate at pressure in excess of 50 bars, the performance of venturi scrubbers is predicted to be even worse. There is insufficient mixing between the gas and liquid at times. There is excessive liquid carryover with high velocity gas. And there is loss of scrubbing performance at operating conditions away from designed conditions. This is because droplet atomization and condensations behaviors change significantly at non-ideal operating conditions.
Venturi scrubbing is a well known and efficient technology offered by equipment suppliers for gasification equipment. Although, the technology is mainly offered for lower pressure ranges and the possibility of having a technology for high pressure and reduced pressure losses would provide substantial benefits to the overall process with reduced need for raw gas compression further downstream. Standard venturi scrubber designs are limited to operating pressures of the gas to be cleaned under 15 bar.